Quasi-Geostationary Observations of CO 2 > from a Highly Elliptical Orbit

Quasi-geostationary observations of

CO2 from a highly elliptical orbit (HEO): a po ten tial meth od f or

monitoring northern CO2 fluxes Ray Nassar1*, Chris Sioris2, John C. McConnell2, Dylan B.A. Jones3

1EiEnvironmen tCdt Canada, 2YkUiYork Univers ity, 3UiUnivers ity o fTf Toron to *[email protected]

IWGGMS-9, Yokohama, Japan , 2013 -05-30 Carbon Cycle at Northern Latitudes

• Declining Arctic sea-ice

• Increasing anthropogenic activity, shipping and resource extraction (oil sands ~57°N)

• Permafrost soil 1672 PgC, emissions of 4 to 104±34 PgC by 2100 (Schaefer et al., 2011)

Boreal Forests UNEP/GRID-Arendal Maps and Graphics Library http://maps.grida.no/go/graphic/boreal-forest-extent Satellite Orbits and Coverage

• Low Earth Orbit (LEO) • Geostationary Orbit (GEO) • Near-polar plane • Near-equatorial plane ~35,800 km altitude • If sun-synchronous, • Synchronized with Earth rotation to give Earth’s rotation gives continuous sampling over selected area global sampling but only (<60°N/S) at a fixed overpass time • TEMPO / GEO-CAPE, Sentinel-4, GEMS for Tropospheric Chemistry

GOSAT (NIES v2.00 2009 -08 averaged at 0.9° x0.9x 0.9°) Satellite Orbits and Coverage

• WMO Vision for the Global Observinggy System (GOS ) in 2025 • Conservation of angular momentum requires faster motion when close to Earth (perigee), slower motion when far from Earth (apogee) Apogee • 12-24 hour orbit with apogees slightly higher than GEO

Three Apogee Orbit (16-hr)

Perigee Trishchenko et al. (2011), J. Atmos. Ocean. Tech. Polar Communications and Weather (()PCW)

• Canadian Space Agency led mission with 2 satellites in Highly Elliptical Orbit (HEO) under consideration for launch ~ 2020

• Weather - Environment Canada – Operational meteorological imaging instruments for northern latitudes • Communications - Department of National Defence – Increase northern communications capability

• CSA is also considering additional science instruments

• Weather, Climate and Air quality (WCA) mission concept is an atmospheric research option that completed Phase A last year, under the Polar Highly Elliptical Orbit Science (PHEOS) program PHEOS-WCA Instrument Configurations

• Fourier Transform Spectrometer (FTS) • UV-Visible Spectrometer (UVS) Optimal Configuration CSA Allocations All Bands Configuration

Size: Compliant Configuration 30 x 30 x 30 cm3 (27 000 cm3)

M50kMass: 50 kg Power: 100 W FTS (aperture 15 cm) with UVS, 85 kg ~103 800* cm3 FTS (aperture 10 cm) with UVS, 45 kg FTS (aperture 10 cm) ~35 128* cm3 No O2 A band or SWIR CO2 O2 A band and SWIR CO2 No UVS, 37 kg ~25 184* cm3 *volumes shown with 20% contingency Observing System Simulation Experiment (OSSE)

• Objective: Compppare the potential information contributed for constrainin g CO2 surface fluxes at northern latitudes from HEO vs. LEO

• Approach:

– Run a model (GEOS-Chem) simulation to obtain a CO2 distribution to use as the ‘Truth’

– Create ‘synthetic observations’ for a LEO mission (GOSAT) and a HEO mission (PHEOS-WCA) by sampling the model at hypothetical observation locations/times then adding noise

– Assimilate each set of synthetic observations to get optimized

estimates of CO2 fluxes and assess posterior flux precision and bias relative to the ‘Truth’ Generating Synthetic Observations

Recreated GOSAT orbit using SPENVIS (ESA), 3 cross track obs: orbit track, ±263 km, glint subsolar±20° Three-APogee (TAP) orbit

2 satellites, 8h apart in co-planar 16h orbit Apogee ~43,500 km, Perigee ~8100 km 3 Apogees/day (8:00 and 16:00 local time) observing ±4 h from apogee giving up to 16 h of data per 48 h per region

Each region/apogee: 48 scans for 100 sec each, consisting of 56x56 array of 10x10 km2 pixels. Checkerboard pattern of data-thinning to meet downlink requirement, and obtibservations every other repeatltt cycle to accommod dtthbiate other observing pr iitiiorities Solar Zenith Angle, Albedo, Cloud

Calculated Solar Zenith Angle (SZA) for each obs and only retained when SZA < 85° Spectral Albedo Values from MODTRAN AVHRR* 1°x1° surface types

*Advanced Very High Resolution Radiometer

GEOS-5 Cloud Fraction 0.5x0.67 01 Signal-to-noise ratio depends on albedo of surface for each band.

Nadir XCO2 retrievals over ocean, sea-ice and old snow are assumed unlikely. Used GOSAT v2. 0 averaging kernels and covariances for these surface types, scaled according to SNRs (reduced precision by factor of 2 over seasonal snow). SNR Comparison to Estimate Precision

Instrument Altitude Aperture Scan 1.61 Assumed SZA SNR Source (km) (cm) Time m albedo at at (s) res 1.61 m 1.61 (cm-1) m TANSO-FTS 665. 96 686.8 4 0200.20 030.3 30° > 300 Yokota et al. (2009) SOLA 60° > 228 Calculated

PHEOS-FTS 41, 200 15. 0 100 0250.25 040.4 60° > 150 Phase-A (max closure report Optimal (2012) 42,500) (85 kg) 0.3 > 134 Calculated

PHEOS-FTS 41,200 10.0 100 0.25 0.4 60° > 100 Phase-A (max closure report All-band (2012) 42,500) (45 kg) 030.3 >91> 91 Calculated

SZA change cos(60 ) cos(30 )  0.7598 Albedo change 0.30 0.40  0.8660 Number of Observations

Post-Filtered

~14,000 early afternoon obs/month from GOSAT Up to 1.8 million daytime obs/month from HEO (with 2D detector array) Biospheric CO 2 Flux Uncertainties

Lower annual flux uncertainties from HEO Biospheric CO 2 Flux Biases

Lower annual flux biases from HEO Could we detect CO2 emissions from permafrost thaw?

• Simulated slow emission of CO2 from permafrost thaw: 0.2 PgC Jul- Sep over 6 million km2 (Schuur et al08l. suggest 0.8-1. 1 Pg C/yr by 2100)

• Generated synthetic obs from this simulation and carried out an inversion to quantify these emissions, assuming no prior knowledge

• Although the total (biospheric + permafrost perturbation) fluxes could be constrained within ~2% and assigned to the proper spatial region, distinguishing permafrost emissions from background biospheric fluxes is much like the challenge of separating biospheric fluxes from fossil fuel emissions, making complementary measurements (i.e. CH4, chlorophyll fluorescence, NDVI, Leaf Area Ind ex (LAI), soil moi st ure or f reeze/th aw, … ) ex treme ly va lua ble Summary and Conclusions

• CO2 fluxes at northern high latitudes are important to monitor and HEO all ows quas i-geosttitationary vi ew ing

• OSSEs demonstrate lower CO2 flux uncertainties and biases from the proposed HEO mission relative to GOSAT for northern mid- andhihlid(d high latitudes (account ing for o bs coverage an d sens iiiitivity, SNRs, SZA, surface properties, cloud cover, snow cover, etc.)

• Annual CO2 biospheric flux uncertainties for Canada, Alaska and Northern Eurasia average 39% of those from GOSAT for the Optimal configuration and 57% for a smaller configuration (although transport errors, retrieval biases and horizontal correltilations h ave not tb been account tdf)hed for); however, bene fits cou ld increase for shorter time periods

• Major emissions of CO2 from permafrost thaw could likely be detected from HEO, but complementary measurements would be required to disentangle the permafrost emissions from the background biospheric fluxes